Hi, I've recently tried Phys2D and found it generally good, and possibly applicable to the game I'm making. However I'm troubled by an instability I've observed: When I connect a chain of several objects via FixedJoints--say, four small boxes widely spaced in a U-shape, sort of like in Phys2D's Demo19--and drop the resulting shape onto a floor, it bounces and wiggles a bit, as one might expect, but the bouncing gradually becomes worse until the shapes simply fly out of sight. Demo19 looks deceptively stable in comparison to this scenario, but I tried copying its setup and tweaking it a little, and I reproduced the same thing pretty easily. Why does this happen? Does Phys2D belong to some general class of physics engines of which this sort of instability is a basic feature? Or is it conceivable that somebody could write a nicer, stabler FixedJoint without too much trouble? My game is currently using ODE, which hasn't this problem... though it is very unfortunately saddled with that nasty third dimension. I don't know what people see in that thing.

Special bonus question: Cursory online research suggests that ODE is nondeterministic; experimentation suggests that Phys2D (and therefore perhaps Box2D et al) is deterministic. Is this correct? Is JOODE nondeterministic? My game likes determinism!

I don't remember what determinism is in computer science. I meant that if you set up a physical scenario with ODE, and let it run twice, you'll get two different outcomes. A box that falls on its corner near a ledge might topple off the ledge on one run, and then on the next run, tip back and settle on the ledge. Like this guy says: http://gamecreator.blogspot.com/2007/03/ode-determinism.html

Box2D does appear to be worth trying, so I'll move on to that and keep my Phys2D exploration on hold for now. I know of JBox2D, and I would prefer to use that since it's pure Java--but maybe Java bindings to Box2D itself would also be worthwhile. I don't immediately see any of those around though.

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